1. Field of the Invention
This invention relates to the microencapsulation of antigens for use as therapeutic or prophylactic vaccines.
2. Description of Background and Related Art
Traditional immunization protocols typically require multiple exposures of the patient to the antigen, usually by injections of a vaccine formulation at intervals of weeks or months. There is a need in the art to deliver the antigen of interest to the patient in a formulation which releases the antigen in bursts spaced days to months apart so as to reduce the need for multiple injections. The initial burst of antigen can be augmented by the addition of soluble antigen to the vaccine formulation. The efficacy of such vaccines can be improved further by the addition of an adjuvant, in soluble and/or microencapsulated form.
Recombinant subunit vaccines have been produced for a variety of viruses, including herpes, malaria, hepatitis, foot and mouth disease, and HIV. Currently, gp120 is considered to be a good candidate for an HIV subunit vaccine, because: (i) gp120 is known to possess the CD4 binding domain by which HIV attaches to its target cells, (ii) HIV infectivity can be neutralized in vitro by antibodies to gP 120, (iii) the majority of the in vitro neutralizing activity present in the serum of HIV infected individuals can be removed with a gp120 affinity column, and (iv) the gp120/gp41 complex appears to be essential for the transmission of HIV by cell-to-cell fusion. Recombinant subunit vaccines are described in Berman et al., PCT/US91/02250 (published as number WO91/15238 on 17 Oct. 1991). See also, e.g., Hu et al. Nature 328:721-724, 1987 (vaccinia virus-HIV env recombinant vaccine); Arthur et al. J. Virol. 63(12): 5046-5053, 1989) (purified gp120); and Berman et al. Proc. Natl. Acad. Sci. USA 85:5200-5204, 1988 (recombinant envelope glycoprotein gp120). There have been suggestions in the literature of making a vaccine which is a combination of various HIV isolates or isolate subunits. See e.g. Berman et al., PCT/US91/02250 (published as number WO91/15238 on 17 Oct. 1991) and Rusche et al., PCT/US89/04302 (published as number WO90/03984 on 19 Apr. 1990).
Different antigens can be combined in the formulation, either within the same microspheres or as a mixture of microspheres, to provide a multivalent or multitarget vaccine. Furthermore, as microspheres can be designed to release a second burst of antigen and/or adjuvant (“autoboost”) when desired, a single vaccine preparation can be designed so as to mix populations of microspheres which release their bursts of antigens and/or adjuvants at multiple prescribed intervals when such multiple challenges with antigen and/or adjuvant are desired.
Preferred adjuvants for use in the compositions and methods of the instant invention include saponins and their derivatives. For example, U.S. Pat. No. 5,057,540 discloses the uses of Quillaja saponins, a mixture of striterpene glycosides extracted from the bark of the tree Quillaja saponaria, as immune adjuvants. Saponins can be isolated from other plants, such as soybeans (U.S. Pat. No. 4,524,067). White et al. (Immunology of Proteins and Peptides VI, ed. M. Z. Atassi, Plenum Press, NY, 1991) disclose the use of QS21 as an adjuvant for a T-independent antigen. Wu et al. (J. Immunol. 148:1519-1525, 1992) disclose the use of QS21 as an adjuvant for the HIV-1 envelope protein gp160 in mice. Newman et al. (AIDS Research and Human Retroviruses 8:1413-1418, 1992) disclose the use of QS21 as ar: adjuvant for the HIV-1 envelop protein gp160 in rhesus macaques. Kensil et al. (J. Am. Vet. Med. Assoc. 199:1423-1427, 1991) disclose the use of QS21 as an adjuvant for the feline leukemia virus subgroup A gp70 protein.
Polymer matrices for forming microspheres are also described in the literature. For example, Chang et al. (Bioengineering 1:25-32, 1976) disclose semipermeable microspheres containing enzymes, hormones, vaccines, and other biologicals. U.S. Pat. No. 5,075,109 discloses a method of potentiating an immune response by administering a mixture of at least two populations of microspheres containing bioactive agents such that one of the microsphere populations is sized between about 1 to 10 μm. U.S. Pat. No. 4,293,539 discloses a controlled release formulation of an active ingredient in a copolymer derived from about 60 to 95 weight percent lactic acid and about 40 to about 4 weight percent glycolic acid. U.S. Pat. No. 4,919,929 discloses the administration of an antigenic substance in a shaped structure of a biocompatible matrix material. U.S. Pat. No. 4,767,628 discloses composition comprising an active, acid stable polypeptide and a polylactide, which when placed in an aqueous physiological environment release the polypeptide at an approximately constant rate in an essentially monophasic manner. U.S. Pat. No. 4,962,091 discloses a microsuspension of water soluble macromolecular polypeptides in a polylactide matrix. U.S. Pat. Nos. 4,849,228 and 4,728,721 disclose a biodegradable, high molecular weight polymer characterized in that the content of water-soluble low molecular weight compounds, as calculated on the assumption that such compounds are monobasic acids, is less than 0.01 mole per 100 grams of high molecular weight polymer. U.S. Pat. Nos. 4,902,515 and 4,719,246 disclose polylactide compositions containing segments of poly(R-lactide) interlocked with segments of poly(S-lactide). U.S. Pat. No. 4,990,336 discloses a multiphasic sustained release system comprising allergen extract encapsulated in microspheres of bioerodible encapsulating polymer which permits a sustained, multiphasic release of the allergen. This system includes a first portion of allergen extract that upon injection is capable of being released in a manner whereby initial allergenicity is minimized to producing a mild local reaction similar to that normally observed with low doses of conventional allergen administration, and secondary portions of allergen extract that provide a substantially higher level of allergen extract in doses that could provide a serious reaction in the patient, but for the release of the first portion of allergen extract. U.S. Pat. No. 4,897,268 discloses a microcapsule delivery system wherein the ingredients are encapsulated in biodegradable copolymer excipients of varying mole ratios, such that delivery of the ingredients occurs at a constant rate over a prolonged period of time.
Various water-in-oil emulsions are described in the literature. Thus, for example, U.S. Pat. Nos. 4,917,893 and 4,652,441 disclose a microcapsule produced by preparing a water-in-oil emulsion comprising an inner aqueous layer containing a water-soluble drug, a drug-retaining substance, and an oil layer containing a polymer substance; the inner or aqueous layer is thickened or solidified to a viscosity of not lower than about 5000 centipoises. The resulting emulsion is subjected to in-water drying. U.S. Pat. No. 4,954,298 discloses the production of microcapsules by preparing a water-in-oil emulsion composed of a water-soluble drug-containing solution as the inner aqueous phase and a polymer-containing solution as the oil phase, dispersing the emulsion in an aqueous phase and subjecting the resulting water-in-oil-in-water emulsion to an in-water drying, wherein the viscosity of the water-in-oil emulsion used in preparing the water-in-oil-in-water emulsion is adjusted to about 150 to about 10,000 centipoises.
Accordingly, it is an object of the invention to provide a microencapsulated vaccine formulation, which can include one or more adjuvants.
It is another object of the invention to provide a vaccine for the prophylaxis and/or treatment of HIV infection.
It is a further object of the invention to provide a method for producing microspheres.
These and other objects will become apparent to those of ordinary skill in the art.